When such glass flakes are dispersed in, for example, a resin composition (resin matrix), a resin mold product obtained from the resin composition will have increased strength and dimensional accuracy. Further, glass flakes are blended with paint as lining and applied to metal or a concrete surface. The glass flakes have a metallic color produced by coating their surfaces with a metal. Further, the surfaces of the glass flakes may be coated by a metal oxide to have an interference color resulting from interference of reflection light. In this manner, glass flakes coated by a metal coating or a metal oxide coating is preferable for use as a luster pigment. Luster pigment using such glass flakes is preferably used for applications in which the color tone and luster are important, such as paint and cosmetics.
A glass flake is fabricated by inflating a molten glass base material with an injection nozzle to form a balloon-shaped hollow glass film and then crushing the hollow glass film with a pressing roller, for example. When such a fabrication process is taken into account, it is required that glass flakes have superior meltability, satisfactory formability, a suitable temperature-viscosity property, and a devitrification temperature that is lower than the working temperature. The working temperature is the temperature when the viscosity of glass is 100 Pa·s (1000 P). Further, the devitrification temperature is the temperature at which crystals form and start to grow in the molten glass base material.
For the temperature-viscosity property, it is preferable that the working temperature be less than or equal to 1300° C. since the glass flakes become difficult to form, particularly, when the working temperature becomes too high. A lower working temperature for glass decreases the cost of fuel when melting the glass crude material. This also decrease the thermal damage caused to a kiln or fabrication apparatus of the glass flakes and thereby allows for the kiln or fabrication apparatus to have a longer life.
Further, when forming a metal coating or a metal oxide coating on glass flakes, the glass flakes may undergo a high-temperature treatment. Additionally, glass flakes or coated glass flakes may be blended with paint and undergo a high-temperature treatment for applications such as baking finishing. Accordingly, glass flakes require sufficient heat resistance. Soda-lime glass, which is typically used as a so-called sheet glass composition, includes a large amount of alkali metal oxide and does not have sufficient heat resistance. When considering the application of glass flakes blended with paint or cosmetics, a coating film or coating would require acid resistance, alkali resistance, and the like. Hence, the glass flakes would require high chemical durability.
To meet these requirements, the applicant of the present application has suggested glass flakes that will now be described. For example, patent document 1 suggests glass flakes that specify the content of silicon dioxide (SiO2), the total content of silicon dioxide and aluminum oxide (Al2O3), the total content of magnesium oxide (MgO) and calcium oxide (CaO), and the total content of lithium oxide (Li2O), sodium oxide (Na2O), and potassium oxide (K2O).
Patent document 2 suggests glass flakes that specify the total content of oxide magnesium and calcium oxide, the total content of lithium oxide and sodium oxide, and the content of titanium dioxide (TiO2).